Approximately two million cataract surgery procedures are performed in the United States annually. The procedure generally involves making an incision in the anterior lens capsule to remove the cataractous crystalline lens and implanting an intraocular lens in its place. The power of the implanted lens is selected (based upon pre-operative measurements of ocular length and corneal curvature) to enable the patient to see without additional corrective measures (e.g., glasses or contact lenses). Unfortunately, due to errors in measurement, and/or variable lens positioning and wound healing, about half of all patients undergoing this procedure will not enjoy optimal vision without correction after surgery. Brandser et al., Acta Ophthalmol Scand 75:162–165 (1997); Oshika et al., J Cataract Refract Surg 24:509–514 (1998). Because the power of prior art intraocular lenses generally cannot be adjusted once they have been implanted, the patient typically must choose between replacing the implanted lens with another lens of a different power or be resigned to the use of additional corrective lenses such as glasses or contact lenses. Since the benefits typically do not outweigh the risks of the former, it is almost never done.
One solution to this problem has been the development of light adjustable intraocular lenses such as those disclosed in U.S. Pat. No. 6,450,642. The lenses described therein are formed from a polymer matrix having photopolymerizable macromers dispersed therein. The photopolymerization of the macromers induces changes in one or more properties of the lens including changes in the optical properties. The lenses, however, require that the macromers be fully consumed in a “lock-in” step preventing unintentional changes in the lens by exposure to UV or ambient light. This exhaustion of the macromers prevents further adjustments to the lens after the initial series of corrections.
A potential method for eliminating the need for a lock-in step is through the use of two photon initiators such as those described and disclosed in U.S. Pat. Nos. 6,267,913; 6,316,153; 6,402,037; 6,555,682; and 6,566,529 as well as published U.S. applications 2002/0185634 and 2003/0052311. The chromophores described in these applications require the use of high intensity light to trigger a release of energy sufficient to initiate a polymerization reaction. While these materials can be used, they are generally not compatible with the materials used to make light adjustable lenses such as siloxanes or acrylates. This incompatibility reduces the optical clarity of the materials and can result in the leaching of the initiators from the lens. This makes these initiators unacceptable for use in optical elements especially contact lenses or intraocular lenses.
It is therefore desirable to provide a photoinitiator that is triggered by light with an intensity greater than ambient light that is compatible with the base material of the light adjustable composition or article.